Since the 1930s it has been known that injury or ablation of the sympathetic nerves in or near the outer layers of the renal arteries can dramatically reduce high blood pressure. As far back as 1952, alcohol has been used in animal experiments. Specifically Robert M. Berne in “Hemodynamics and Sodium Excretion of Denervated Kidney in Anesthetized and Unanesthetized Dog” Am J Physiol, October 1952 171:(1) 148-158, describes painting alcohol on the outside of a dog's renal artery to produce denervation.
At the present time, physicians often treat patients with atrial fibrillation (AF) using radiofrequency (RF) catheter systems to ablate conducting tissue in the wall of the left atrium of the heart around the ostium of the pulmonary veins. Similar technology, using radiofrequency energy, has been successfully used inside the renal arteries to ablate sympathetic and other nerve fibers that run in the outer wall of the renal arteries, in order to treat high blood pressure. In both cases these are elaborate and expensive catheter systems that can cause thermal, cryoablative, or other methods to injure surrounding tissue. Many of these systems also require significant capital outlays for the reusable equipment that lies outside of the body, including RF generation systems and the fluid handling systems for cryoablative catheters.
Because of the similarities of anatomy, for the purposes of this disclosure, the term target wall will refer here to either wall of a pulmonary vein near its ostium for AF ablation applications or the wall of the renal artery, for hypertension or congestive heart failure (CHF) applications.
In the case of atrial fibrillation ablation, the ablation of tissue surrounding multiple pulmonary veins can be technically challenging and very time consuming. This is particularly so if one uses RF catheters that can only ablate one focus at a time. There is also a failure rate using these types of catheters for atrial fibrillation ablation. The failures of the current approaches are related to the challenges in creating reproducible circumferential ablation of tissue around the ostium (peri-ostial) of a pulmonary vein. There are also significant safety issues with current technologies related to very long fluoroscopy and procedure times that lead to high levels of radiation exposure to both the patient and the operator, and may increase stroke risk in atrial fibrillation ablation.
There are also potential risks using the current technologies for RF ablation to create sympathetic nerve denervation from inside the renal artery for the treatment of hypertension or congestive heart failure. The short-term complications and the long-term sequelae of applying RF energy from inside the renal artery to the wall of the artery are not well defined. This type of energy applied within the renal artery, and with transmural renal artery injury, may lead to late restenosis, thrombosis, renal artery spasm, embolization of debris into the renal parenchyma, or other problems inside the renal artery. There may also be uneven or incomplete sympathetic nerve ablation, particularly if there are anatomic anomalies, or atherosclerotic or fibrotic disease inside the renal artery, such that there is non-homogeneous delivery of RF energy. This could lead to treatment failures, or the need for additional and dangerous levels of RF energy to ablate the nerves that run along the adventitial plane of the renal artery.
The Ardian system for RF energy delivery also does not allow for efficient circumferential ablation of the renal sympathetic nerve fibers. If circumferential RF energy were applied in a ring segment from within the renal artery (energy applied at intimal surface to kill nerves in the outer adventitial layer) this could lead to even higher risks of renal artery stenosis from the circumferential and transmural thermal injury to the intima, media and adventitia. Finally, the “burning” or the inside of the renal artery using RF ablation can be extremely painful. Thus, there are numerous and substantial limitations of the current approach using RF-based renal sympathetic denervation. Similar limitations apply to Ultrasound or other energy delivery techniques.
The BULLFROG® micro infusion catheter described by Seward et al in U.S. Pat. Nos. 6,547,803 and 7,666,163 which uses an inflatable elastic balloon to expand a single needle against the wall of a blood vessel could be used for the injection of a chemical ablative solution such as alcohol but it would require multiple applications as it does not describe or anticipate the circumferential delivery of an ablative substance around the entire circumference of the vessel. The most number of needles shown by Seward is two and the two needle version of the BULLFROG® would be hard to miniaturize to fit through a small guiding catheter to be used in a renal artery. If only one needle is used, controlled and accurate rotation of any device at the end of a catheter is difficult at best and could be risky if the subsequent injections are not evenly spaced. This device also does not allow for a precise, controlled, and adjustable depth of delivery of a neuroablative agent. This device also may have physical constraints regarding the length of the needle that can be used, thus limiting the ability to inject agents to an adequate depth, particularly in diseased renal arteries with thickened intima. Another limitation of the BULLFROG® is that inflation of a balloon within the renal artery can induce stenosis due to balloon injury of the intima and media of the artery, as well as causing endothelial cell denudation.
Jacobson and Davis in U.S. Pat. No. 6,302,870 describe a catheter for medication injection into the inside wall of a blood vessel. While Jacobson includes the concept of multiple needles expanding outward, each with a hilt to limit penetration of the needle into the wall of the vessel, his design depends on rotation of the tube having the needle at its distal end to allow it to get into an outward curving shape. The hilt design shown of a small disk attached a short distance proximal to the needle distal end has a fixed diameter which will increase the total diameter of the device by at least twice the diameter of the hilt so that if the hilt is large enough in diameter to stop penetration of the needle, it will significantly add to the diameter of the device. For either the renal denervation or atrial fibrillation application, the length of the needed catheter would make control of such rotation difficult. In addition, the hilts which limit penetration are a fixed distance from the distal end of the needles. There is no built in adjustment on penetration depth which may be important if one wishes to selectively target a specific layer in the blood vessel or if one needs to penetrate all the way through to the volume past the adventitia in vessels with different wall thicknesses. Jacobson also does not envision use of the injection catheter for denervation. Finally, in FIG. 3 of Jacobson, when he shows a sheath over expandable needles, there is no guide wire and the sheath has an open distal end which makes advancement through the vascular system more difficult. Also, the needles, if they were withdrawn completely inside of the sheath, could, because of the hilts, get stuck inside the sheath and be difficult to push out.
The prior art also does not envision use of anesthetic agents such as lydocaine which if injected first or in or together with an ablative solution can reduce or eliminate any pain associated with the denervation procedure.
As early as 1980, alcohol has been shown to be effective in providing renal denervation in animal models as published by Kline et al in “Functional re-innervation and development of supersensitivity to NE after renal denervation in rats”, American Physiological Society 1980:0363-6110/80/0000-0000801.25, pp. R353-R358. While Kline states that “95% alcohol was applied to the vessels to destroy any remaining nerve fibers, using this technique for renal denervation we have found renal NE concentration to be over 90% depleted (i.e. <10 mg/g tissue) 4 days after the operation” Again in 1983, in the article “Effect of renal denervation on arterial pressure in rats with aortic nerve transaction” Hypertension, 1983, 5:468-475, Kline again publishes that a 95% alcohol solution applied during surgery is effective in ablating the nerves surrounding the renal artery in rats. While drug delivery catheters such as that by Jacobson, designed to inject fluids at multiple points into the wall of an artery, have existed since the 1990's and alcohol is effective as a therapeutic element for renal denervation, there is need for an intravascular injection system specifically designed for the PeriVascular circumferential ablation of sympathetic nerve fibers in the outer layers' around the renal arteries with adjustable penetration depth to accommodate variability in renal artery wall thicknesses.
The prior art also does not envision use of anesthetic agents such as lidocaine which, if injected first or in or together with an ablative solution, can reduce or eliminate any pain associated with the denervation procedure.
McGuckin, in U.S. Pat. No. 7,087,040, describes a tumor tissue ablation catheter having three expandable tines for injection of fluid that exit a single needle. The tines expand outward to penetrate the tissue. The McGuckin device has an open distal end that does not provide protection from inadvertent needle sticks from the sharpened tines. In addition the McGuckin device depends on the shaped tines to be of sufficient strength that they can expand outward and penetrate a the tissue. To achieve such strength tines would not be small enough so as to have negligible blood loss when retracted back following fluid injection for a renal denervation application. There also is no workable penetration limiting mechanism that will reliably set the depth of penetration of the injection egress from the tines with respect to the inner wall of the vessel, nor is there a pre-set adjustment for such depth. For the application of treating liver tumors, the continually adjustable depth of tine penetration makes sense where multiple injections at several depths might be needed; however for renal denervation, being able to accurately dial in the depth is critical so as to not infuse the ablative fluid too shallow and kill the media of the renal artery or too deep and miss the nerves that are just outside or in the outer layer of the renal artery.
Finally Fischell et al in U.S. patent application Ser. Nos. 13/092,363, 13/092,363 describe expandable intravascular catheters with expandable needle injectors. In Ser. No. 13/092,363 the Fischells disclose an intravascular catheter with a sheath that, unlike Jacobson, has a closed configuration that completely encloses the sharpened needles to protect health care workers from needle stick injuries and blood borne pathogens. The Fischell application Ser. Nos. 13/092,363, 13/092,363, however show only designs to operate into the wall of the left atrium around the ostium of a pulmonary vein or into the wall of the aorta around the ostium of a renal artery and not from inside a vessel.